On Sun, Dec 11, 2011 at 02:40:58PM +0200, Dor Laor wrote:

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When a guest kernel is stopped by the host hypervisor it can look like a soft
lockup to the guest kernel.  This false warning can mask later soft lockup
warnings which may be real.  This patch series adds a method for a host
hypervisor to communicate to a guest kernel that it is being stopped.  The
final patch in the series has the watchdog check this flag when it goes to
issue a soft lockup warning and skip the warning if the guest knows it was
stopped.

It was attempted to solve this in Qemu, but the side effects of saving and
restoring the clock and tsc for each vcpu put the wall clock of the guest behind
by the amount of time of the pause.  This forces a guest to have ntp running
in order to keep the wall clock accurate.

Guests need to run NTP regardless, not only the virtualization layer
add some skew, the physical world is not that perfect.
btw: traditional NTP client won't sync the time automatically if the
diff is > 0.5%.

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Having this controlled from userspace means it doesn't work for SIGSTOP
or for long scheduling delays.  What about doing this automatically
based on preempt notifiers?

Isn't it solved by steal time?

No.